A solecism is a misuse or misapplication of rules or customs. It’s often understood to mean the misuse of language or grammar, often unintentional and generally unacceptable. Solecisms are usually committed out of ignorance.
For example, American schoolchildren are vigorously taught not to say “Me and John went to the store,” because “me” is an object pronoun, not a subject pronoun. They’re taught that the proper construction is “John and I went to the store.” Unfortunately, what they actually learned, apparently, is that “Me and John” is incorrect under any circumstance, and in a classic example of hypercorrection, will think they're avoiding the "John and me" solecism by saying something like “Harry was talking to John and I.”
Double negatives are another very common type of solecism: “We ain’t got no bananas,” technically speaking, actually expresses that we do have bananas, if one considers that “no bananas” is the same as “zero bananas” and “ain’t got” is the opposite of “have.” Of course, solecisms are often understood as meant. When a shopkeeper says “We ain’t got no bananas,” the savvy shopper will avoid correcting his grammar and simply seek out bananas elsewhere. Some solecisms are illogical: “I could care less,” for instance, is an unfortunate mutilation of “I couldn’t care less.” The two are opposite in meaning on paper, yet some people use the former when they mean the latter.
Solecisms can also include the misuse of words. For instance, when a disaster is anticipated, authorities might call for the evacuation of a town, but people are not evacuated — they may depart, be moved, or transported, but evacuate means to empty a thing or a place of its contents or inhabitants. “Literally” is frequently abused as equivalent to “figuratively” — as in, for example, “The speaker got so excited his head literally exploded!” “Unique” is frequently abused by modifiers — if unique means “one of a kind,” calling something “very unique" or "singularly unique" as many do just doesn't make sense.
The one thing “irregardless,” “preventative” and “orientate” have in common is that they’re not actually words. They’ve come into being as a result of misuse of their correct counterparts: “regardless,” “preventive” and “orient.” Quite a number of people use the incorrect versions in place of the actual words.
Some solecisms are pet peeves for many. The misuse of the reflexive pronoun “myself” is one. Such constructions as “How’s yourself” and “Harry and myself went to the store” fuel a never-ending debate between those who consider it abuse of the language and those who insist that the dynamic nature of the language requires that prescriptive rules established in centuries past should be at least relaxed for the 21st century.
In everyday conversation, solecisms are usually accepted, though, even while they’re considered unacceptable in prose. Artistic license also permits solecisms in the world of entertainment, and “I Can’t Get No Satisfaction,” for instance, is widely considered an acceptable expression of Mr. Jagger’s level of frustration. William Shakespeare penned thousands of solecisms, but the conventional wisdom is that he did so deliberately, often to highlight aspects of his characters’ personalities.
Solecisms aren’t restricted to grammatical errors. A breach of etiquette is also considered a solecism. This can be something as inconsequential as using the wrong fork to eat one’s salad or wearing white after Labor Day, or something as egregious as addressing England’s queen as “Liz” without having first been invited to do so.